For the past several years, MEMS structures have been playing an increasingly important role in consumer products. For example, MEMS devices, such as sensors, detectors and mirrors, can be found in products ranging from air-bag triggers in vehicles to displays in the visual arts industry. As these technologies mature, the demands on precision and functionality of the MEMS structures have escalated. For example, optimal performance may depend on the ability to fine-tune the characteristics of various components of these MEMS structures. Furthermore, consistency requirements for the performance of MEMS devices (both intra-device and device-to-device) often dictates that the processes used to fabricate such MEMS devices need to be extremely sophisticated.
A recent fabrication challenge in the field MEMS devices is the formation of MEMs resonators. A typical MEMS resonator has at least a portion of the MEMS structure “suspended” above a substrate, i.e. not directly attached to the substrate, thus requiring some form of an anchor to couple the resonator with the underlying substrate. Two methods used to fabricate such resonators with anchors include 1) a total damascene approach and 2) an anchor-then-beam approach. Both methods, however, have their limitations.
A total damascene approach has been used to fabricate a MEMS resonator anchored to a substrate. FIGS. 1A-C illustrate a cross-sectional view representing a series of steps in a total damascene approach for fabricating a MEMS structure having a member coupled to a substrate, in accordance with the prior art.
Referring to FIG. 1A, a trench 106 consisting of a first feature 108 and a second feature 110, usually patterned in two separate steps, is patterned into release layer 104 above a substrate 102. Trench 106 is then filled with a structural layer 112, usually by blanket deposition of a material layer followed by planarization of the material layer, as depicted in FIG. 1B. Referring to FIG. 1C, release layer 104 is removed to provide a MEMS resonator 114 comprised of a resonating member 116 (formed from second feature 110 of trench 106) connected to substrate 102 by an anchor 118 (formed from first feature 108 of trench 106). One drawback to this approach is that the composition of the anchor is limited to being the same as the composition of the resonating member.
An anchor-then-beam approach has also been used to fabricate a MEMS resonator anchored to a substrate. FIGS. 2A-D illustrate a cross-sectional view representing a series of steps in an anchor-then-beam approach for fabricating a MEMS structure having a member coupled to a substrate, in accordance with the prior art.
Referring to FIG. 2A, an anchor 218 is provided in a release layer 204 above a substrate 202, either by a single-damascene technique or by subtractively forming anchor 218 and subsequently depositing and planarizing the material used to form release layer 204. A structural layer 212 is then deposited above anchor 218 and release layer 204, as depicted in FIG. 2B. Referring to FIG. 2C, structural layer 212 is patterned to form a resonating member 216 above release layer 204 and aligned with anchor 218. Release layer 204 is then removed to provide a MEMS resonator 214 comprised of resonating member 216 connected to substrate 202 by anchor 218, as depicted in FIG. 2D. One drawback to this approach is that the structural integrity of the MEMS resonator is dependent upon a single anchor/resonating member interface 220.
Thus, a MEMS coupler is described herein, along with a method to fabricate a MEMS structure having such a coupler.